1. Field of the Invention
The present invention relates to a display device such as a liquid crystal display device, for example, and to a manufacturing method thereof.
2. Description of the Related Art
Recently, the number of display devices each having a frontal panel such as a touch panel or a decorated panel on a liquid crystal display module as a device for display is increasing. A touch panel is an input interface component. A decorated panel is a reinforced glass or the like on which printing is applied for decoration for design qualities and protection of the display face.
When the frontal panel is loaded on the liquid crystal display module, there is normally an air layer exiting between the liquid crystal panel surface and the frontal panel. Thus, due to a difference in the refractive indexes of the frontal panel (e.g., a glass substrate) and the air layer, light is reflected in the interface between those. Due to the interface reflection, visibility of the displayed images becomes deteriorated greatly particularly under an open air environment.
For this, there is proposed a technique for improving the visibility of the displayed images by suppressing the interface reflection through filling an optical elastic resin exhibiting a refractive index close to that of the glass substrate of the frontal panel in the air layer portion and laminating the liquid crystal panel and the frontal panel. This technique for laminating the whole surfaces is called optical-bonding or direct-bonding, which provides not only an optical effect but also a mechanical effect such as preventing scattering when the frontal panel is cracked and improving the shock resistance. Therefore, such technique has come to be employed broadly.
Further, even with outer circumference lamination (referred to as “air gap bonding” for convenience hereinafter) of the square-shaped frontal panel and the display module with the air layer provided therebetween, deterioration in the display quality caused by foreign matters inserted into the inside of the display face is an issue. Thus, even in such case, it is required to improve the display quality not only by simply pasting the frontal panel to the display module but by employing some kinds of devising.
Next, a display device of Related Technique 1 will be described by referring to FIG. 17 to FIG. 19C.
As shown in FIG. 17, a display module 70 includes: a display panel 10 such as a liquid crystal panel; a backlight 71 as a casing for housing the display panel 10; and a bezel 20 for covering the fringe of the display panel 10. The display panel 10 is constituted with: polarization plates 12, 15; a CF (Color Filter) substrate 13; a TFT (Thin Film Transistor) substrate 14; an FPC (Flexible Printed Circuit) substrate 17; and the like. The bezel 20 includes a frame part 21 and an aperture end 22.
As shown in FIG. 18, a display device 201 of Related Technique 1 is acquired by: forming a frame-like resin member 45 on the display module 70; applying an optical elastic resin (referred to as “OCR (Optically Clear Resin)” hereinafter) 50 inside thereof; and laminating a frontal panel 30 thereto from the above. The frontal panel 30 is a touch panel, which is constituted with a cover panel 31, a sensor glass 32, an FPC substrate 33, and the like. As described, the technique which laminates the whole surfaces of the display module 70 and the frontal panel 30 via a UV (Ultra Violet) curable OCR 50, for example, is the above-described optical-bonding.
As shown in FIG. 19B, with the optical-bonding, it is typical to form a dam-like resin member 45 formed with the same or a similar material as that of the OCR 50 in a gap 72 between the bezel 20 and the display panel 10 at the aperture end 22. The resin member 45 is formed to prevent the OCR 50 from permeated into the display module 70 from the gap 72 (for sealing up). Further, the resin member 45 is formed on a light-shielding film 16 between the aperture end 22 and a display region 18 since it is easily recognized as display unevenness when formed to cover the display region (pixel region) 18.
An optical sheet 73 and a backlight chassis 74 shown in FIG. 19B are a part of the backlight 71 shown in FIG. 17. Further, the polarization plate 15 shown in FIG. 19B is a part of the display panel 10.
Next, the process of the optical-bonding will be described by referring to FIG. 20A to FIG. 20G. First, the display module 70 is prepared (FIG. 20A). Subsequently, the UV curable resin is applied by a dispenser 91, and UV light is irradiated by following the applied track by using a spot UV light source 92 to tentatively cure the resin. Through keeping the applied shape, the resin member 45 is formed (FIG. 20B). Thereafter, the OCR 50 for pasting the whole surfaces is applied by slit coating, for example (FIG. 20C). A UV curable adhesive 65, for example, is disposed on the bezel in the outer circumference of the resin member 45 as necessary (FIG. 20D), and the frontal panel 30 and the display module 70 are laminated under a reduced pressure environment, for example (FIG. 20E). Thereafter, the four corners are tentatively fixed by UV irradiation performed by the spot UV light source 92, for example (FIG. 20F). Further, through irradiating a prescribed UV light amount to the whole surfaces by using a conveyor UV irradiation device or the like including a UV light source 93 for adhesive-curing the frontal panel 30 to the display module 70 so as to acquire the display device 201 (FIG. 20G).
However, there is heaving generated in the bezel 20 of the display module 70 shown in FIG. 19A and FIG. 19B because of variation in crafting members and variation in assembling. Thus, due to the heaving of the bezel 20, there is generated variation in the gap 72 between the bezel 20 and the display panel 10. Further, in a large part of the gap 72, the resin member 45 may flow out and permeate into the back face side of the bezel 20 before UV-curing the resin member 45 (this phenomenon is called “sinkage”). As a result, as shown in FIG. 19C, the proper resin member 45 cannot be formed but the gap 75 tends to be formed between the resin member 45 and the aperture end 22. Further, when the gap 75 exists at the time of lamination, the OCR 50 permeates into the inside of the display module 70 from the gap 75. The OCR 50 permeated into the inside of the display module 70 is not cured even after a passage of time since the UV light is not irradiated, and spreads to every gaps within the display module 70. In the worst cases, display fault may be caused because the OCR 50 spreads to the backlight irradiating surface by passing through the back face of the display panel 10 and the optical sheet 73 or the uncured OCR 50 may leak out from the display module 70.
Next, a display device of Related Technique 2 will be described by referring to FIG. 21.
The display device of the Related Technique 2 is designed to overcome an issue of permeation of OCR into the inside of the module (see Japanese Unexamined Patent Publication 2010-66711 (Patent Document 1)). The display device 202 of the Related Technique 2 includes: an optical member 300; a first adhesive 310 (flow-sealing part 311); a second adhesive 320 (applied region 321); a display element 330; a casing 340; a light source 350; a light guide plate 360; an optical film 370; and the like. It is considered with the Related Technique 2 to prevent the uncured second adhesive 320 (applied region 321) from contaminating inside the casing 340 through providing the first adhesive 310 (flow-sealing part 311) along a gap G between the display element 330 and the casing 340 to seal the gap G (see paragraphs 0046 to 0051 and FIG. 2 of Patent Document 1).
However, there are following new issues (1) and (2) in the display device of the Related Technique 2.
(1) As shown in FIG. 21, it is the object of the Related Technique 2 to form the flow-sealing part 311 on the same plane as the display element 330 and the casing 340 to bury the gap G on the plane by the flow-sealing part 311. In the meantime, as shown in FIG. 19B, the Related Technique 1 is targeted for the gap 72 between the aperture end 22 and the display panel 10, i.e., a step between two different planes. That is, there is variation in the steps of the gap 72 of the present invention as described above so that the steps cannot be sealed sufficiently by simply applying a resin (corresponding to the first adhesive 310) along the gap 72. Thus, a space is easily generated between the resin member 45 and the aperture end 22. Further, even if the resin is to be applied along the gap 72, it is necessary to apply the resin by injecting it from the lateral direction of the gap 72. Therefore, it is technically difficult in terms of manufacture to apply the resin on the whole circumference of the steps of the gap 72 with high precision.
(2) As shown in FIG. 21, with the Related Technique 2, stresses (e.g., a pressurized stress and the like applied between the steps of applying the second adhesive 320 and pasting the components) in the manufacturing steps is imposed upon the display element 330 and the casing 340 after forming the flow-sealing part 311. Thus, when there is a step generated between the display element 330 and the casing 340, those are likely to be exfoliated. Specifically, as shown in FIG. 22A to FIG. 22C, let's look into a case where the flow-sealing part 311 of the Related Technique 2 is used for a structure of the present invention. In that case, the flow-sealing part 311 and the aperture end 22 are adhesively joined only by the thickness of the bezel 20 (see FIG. 20A). Therefore, when the stresses in the manufacturing steps described above are applied, the display panel 10 is bent so that the flow-sealing part 311 and the aperture end 22 are easily exfoliated (FIG. 22B). Thus, the OCR 50 leaks out to the back side of the display panel 10. Therefore, the issue of the present invention cannot be overcome by the Related Technique 2.